#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>

int main()
{
	int a[9] = {1,2,3,4,5,1,2,3,4};
	int b = a[0] ^ a[1];
	for (int i = 2; i <= 8; i++)
	{
		b = b ^ a[i];
	}
	printf("%d", b);

	return 0;
}